This invention relates generally to phased array antennas and, more particularly, to phased array antenna systems that must provide multiple beams simultaneously. By adjusting the phase angles of signals received from or transmitted to multiple antenna elements in an antenna array, an antenna control system effectively steers the antenna beam, whether in a receive mode or a transmit mode. In satellite communication systems, it is highly desirable to be able to provide phased array antenna systems with highly agile beams, which can be scanned both rapidly and accurately between beam locations. It is also desirable to provide on-orbit re-configurabilty of such an antenna system, to switch rapidly between different beam configurations as needed.
In both commercial and military satellite communication systems, antenna arrays must be controlled to produce relatively narrow beams, as small as one degree in width. Each narrow beam covers only a relatively small, approximately circular area of the earth's surface. Besides being more energy efficient, the use of narrow beams permits multiple ground stations to use the same radio frequency without conflict. Also modern satellite communication systems need the ability to transmit or receive over multiple beams simultaneously. As the number of required multiple beams increases, so does the complexity of the phased array antenna control circuitry.
In conventional phased array antenna systems, each radiating element in the array has to have an independent radio-frequency (RF) phase shifting circuit for each independent beam to be produced. In an illustrative system to be discussed in more detail below, the array has 547 elements and there is a requirement to produce sixteen independent beams. Thus, 8,752 phase shifting circuits are needed, together with sixteen 547-way RF power combiners to produce the sixteen independent beams. Each phase shifting circuit has to be connected to an appropriate one of the power combiners, creating a maze of crossing lines. Moreover, each of the phase shifting circuits requires its own four-bit control line to provide the requisite beam steering accuracy. The complexity of implementation increases even further as the number of independent beams rises above a modest value.
Accordingly, it will be appreciated that there is a need for a less complex technique to provide multiple independent beams from a phased array antenna system. The present invention is directed to this end.